Objectives:Percent time in therapeutic range (TTR) with warfarin is increasingly used as a performance measure in VA. TTR has attractive features: it is linked to outcomes such as stroke and hemorrhage, can be improved, and is resistant to gaming and perverse incentives. However, during our ongoing intervention to introduce TTR as a quality metric, stakeholders urged adoption of a measure that would be more responsive to process changes in real time. We therefore sought to assess the impact of shortening the conventional measurement period for TTR.

Methods:We examined 124 sites within VA over a 7-year period (FY08-14). TTR has historically been calculated using a 6-month time window. For this study, we varied the duration of time segments (2, 3, 4, 6 months) used to calculate TTR. We compared the results from these 4 permutations on number of patients retained per site, mean and median site TTR, and site performance rankings.

Results:As the calculation window shortened, patients with better control (i.e. higher TTR) were selectively excluded from the measurement, because their laboratory values are more widely spaced. Site mean TTR was highest when the most patients were included (6 months: 950 patients; TTR 65.2%) and lowest when the fewest patients were included (2 months: 567 patients; TTR 60.0%). However, despite these extremes, the 3-, 4-, and 6-month permutations achieved similar results. All three included more than 800 patients per site, with mean TTR across a narrow range (64.9-65.2%). Site rankings were less highly correlated between the 2-month period and longer periods (r = 0.7-0.8), but were otherwise 0.95 or higher, with a nearly perfect correlation (0.985) between the 4- and 6-month periods.

Implications:When using TTR to measure site-level performance, comparable results can be achieved using a 4- or a 6-month measurement period. Based on these results, we recommend the use of a 4-month measurement period for future quality measurement within VA.

Impacts:This study will contribute to the deployment of TTR as a performance measure within VA, by enabling capture of performance improvements within a shorter time frame. Incorporating stakeholder feedback about the design of performance measures can help improve their utility.